A radiation monitor which includes a detection unit and a measurement unit and can select between a normal mode and a check radiation source mode is installed in nuclear reactor facilities, spent fuel reprocessing facilities, and the like (for example, see Patent Documents 1 and 2). The detection unit of the radiation monitor is equipped with: a radiation detector which detects radiation and outputs a detection signal; and a check radiation source irradiation section which irradiates radiation for inspection to the radiation detector by remote operation. The check radiation source irradiation section includes an AC solenoid.
A signal processing section, a calculation section, a mode selection switch, and a circuit protector are installed in the measurement unit of the radiation monitor. The signal processing section measures the radiation by being inputted with the detection signal outputted from the radiation detector. The calculation section converts a measurement value thereof into an engineering value as a radiation dose per unit time and provides an output. A display section displays the engineering value.
The mode selection switch performs selective operation between the normal mode in which normal measurement is performed and the check radiation source mode in which measurement is performed in a state where the radiation for inspection is irradiated to the radiation detector. If the AC solenoid of the check radiation source irradiation section exceeds a set current value, the circuit protector trips a contact thereof to interrupt the current of the AC solenoid by time delay characteristics depending on the size of the current value and mechanically self-maintains its contact state.
“Japan Electric Association Guide (JEAG) 4606-2003, Guideline for radiation monitoring of nuclear power plants” is defined as Japanese domestic guidelines relating to the radiation monitor. When the check radiation source mode is selected, the check radiation source is irradiated to the radiation detector to confirm soundness of the radiation monitor based on the guideline. When there occurs abnormality in the AC solenoid of the check radiation source irradiation section and accordingly an overcurrent flows, the current is interrupted by the circuit protector to protect the radiation detector.